1. Field of Invention
This invention relates to a titanium trichloride catalyst useful as a catalyst component for the stereoregular polymerization of .alpha.-olefins, whereby uniform polymer grains can be given with a high polymerization activity and a high stereoregular polymer ratio, and a process for producing the same.
2. Discussion of Prior Art
As a catalyst used for the stereoregular polymerization of .alpha.-olefins, in general, are known halides of transition metal elements of low valency, for example, .alpha.-type titanium trichloride obtained by reducing titanium tetrachloride with hydrogen, an eutectic substance of .alpha.-titanium trichloride and aluminum chloride, obtained by reducing titanium tetrachloride with aluminum, .delta.-type titanium trichloride obtained by crushing this eutectic substance and the like. As a method of modifying titanium trichloride, it has been proposed to add metal halides alkylaluminum compounds, halogenated hydrocarbons, ethers, esters, ketones, etc., optionally followed by grinding. For example, Japanese Patent Application (OPI) No. 59185/1973, published May 30, 1973, describes a method of modifying .alpha.-type titanium trichloride by crushing .alpha.-type titanium trichloride with halogenated hydrocarbons such as carbon tetrachloride, chloroform, dichloromethane and hexachloroethane. However, this method is disadvantageous in that other type titanium trichlorides than .alpha.-type titanium trichloride cannot be used, preparation of the catalyst is complicated because of requiring a crushing treatment, etc., and the resulting catalyst is unsatisfactory in polymerization activity and stereoregular polymer yielding ratio.
Furthermore, there have been proposed in the art a method comprising reducing titanium tetrachloride with an organo aluminum compound, treating the thus obtained reduced solid containing titanium trichloride with a complexing agent to extract and remove the aluminum compounds and then treating with titanium tetrachloride (Japanese Patent Application (OPI) No. 34478/1972, published Nov. 21, 1972), a method comprising treating the same with carbon tetrachloride (Japanese Patent Application (OPI) No. 112289/1975, published Sept. 3, 1975) and a method comprising reducing titanium tetrachloride with an organo aluminum compound and then treating the thus obtained reduced solid containing titanium trichloride with a mixture of a complexing agent and carbon tetrachloride (Japanese Patent Application Publication No. Sho 52-35350 published Sept. 8, 1977.
Furthermore, in U.S. Pat. No. 3,825,524, there is disclosed a process for producing a titanium trichloride catalyst having high activity which includes extracting a crude titanium trichloride composition, obtained by reducing titanium tetrachloride with an organoaluminum chloride, with a mixed solvent system composed of (i) a main solvent of aliphatic or aromatic hydrocarbons, aromatic chlorinated hydrocarbons or trichloroethylene, and (ii) an auxilliary solvent, including ethers.
However, the first method wherein the after-treatment is carried out using titanium tetrachloride is poor economy since an expensive high concentration solution of titanium tetrachloride is required and the second method wherein the aftertreatment is carried out using carbon tetrachloride is advantageous in that expensive titanium tetrachloride can be substituted by cheap carbon tetrachloride, but is not always satisfactory since the yield of titanium trichloride is low due to the tendency of carbon tetrachloride to dissolve titanium trichloride and the resulting catalyst exhibits a low polymerization activity, low stereoregular polymer yielding ratio and an unfavorable grain shape of polymer.